U.S. patent application number 10/594721 was filed with the patent office on 2007-12-06 for multicolor electroluminescent element.
This patent application is currently assigned to Schreiner Group GmbH & Co., KG. Invention is credited to Manfred Hartmann, Oliver Narwark, Wolfgang Perzlmeier.
Application Number | 20070278943 10/594721 |
Document ID | / |
Family ID | 34979910 |
Filed Date | 2007-12-06 |
United States Patent
Application |
20070278943 |
Kind Code |
A1 |
Hartmann; Manfred ; et
al. |
December 6, 2007 |
Multicolor Electroluminescent Element
Abstract
The electroluminescent (EL) element comprises a transparent
plastic film substrate (1) onto whose rear side a transparent first
electrode layer (2) comprised of indium tin oxide (ITO) is vacuum
sputtered. A first electroluminescent layer (3) with dispersed
electroluminophores (4) is placed on the first electrode layer (2).
This first electroluminescent layer consists of a transparent
matrix (5) into which the electroluminophores (4) are incorporated
(4). The second electrode layer (rear electrode layer) (6) is
placed on the first electroluminescent layer (3) or on an
insulating intermediate layer (not shown) located thereon. This
second electrode layer is insulated toward its side facing away
from the first electroluminescent layer (3) by means of the
insulating layer (7). On the front side, i.e. the visible face, a
third electrode layer (8) comprised of transparent conductive
lacquer is applied to the plastic film substrate (1). A second
electroluminescent layer (9) with dispersed electroluminophores (4)
is placed on the third electrode layer (8). The fourth electrode
layer (10) comprised of transparent conductive lacquer is placed on
said second electroluminescent layer (9) or on an insulating
intermediate layer (not shown) located thereon. This fourth
electrode layer (10) is insulated on the visible face by means of
an insulating layer (11).
Inventors: |
Hartmann; Manfred;
(Ziegelberg/Petershausen, DE) ; Perzlmeier; Wolfgang;
(Landshut, DE) ; Narwark; Oliver; (Munich,
DE) |
Correspondence
Address: |
NIXON PEABODY, LLP
401 9TH STREET, NW
SUITE 900
WASHINGTON
DC
20004-2128
US
|
Assignee: |
Schreiner Group GmbH & Co.,
KG
Bruckmannring 22
Oberschleissheim
DE
85764
|
Family ID: |
34979910 |
Appl. No.: |
10/594721 |
Filed: |
April 4, 2005 |
PCT Filed: |
April 4, 2005 |
PCT NO: |
PCT/EP05/03535 |
371 Date: |
July 25, 2007 |
Current U.S.
Class: |
313/506 |
Current CPC
Class: |
H05B 33/28 20130101;
H05B 33/145 20130101 |
Class at
Publication: |
313/506 |
International
Class: |
H01J 1/70 20060101
H01J001/70 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 22, 2004 |
DE |
10 2004 019 611.7 |
Claims
1. A multicolor electroluminescent element, comprising: a
substrate, which is at least partially transparent over at least
part of its area, having a front side and a rear side, a first
electrode layer situated on the rear side of the substrate, a first
electroluminescent layer, having electroluminophores incorporated
therein, situated on a side of the first electrode layer facing
away from the substrate, a second electrode layer situated on a
side of the first electroluminescent layer facing away from the
substrate, a third electrode layer situated on the front side of
the substrate, a second electroluminescent layer, having
electroluminophores incorporated therein, situated on a side of the
third electrode layer facing away from the substrate, a fourth
electrode layer, situated on a side of the second
electroluminescent layer facing away from the substrate.
2. The multicolor electroluminescent element according to claim 1,
wherein at least one of the second and the fourth electrode layer
is a transparent conductive lacquer layer.
3. The multicolor electroluminescent element according to claim 1,
wherein at least one of the first and third electrode layer is a
transparent conductive lacquer layer.
4. The multicolor electroluminescent element according to claim 2,
wherein at least one of the conductive lacquer layers at least
predominantly comprises an electrically conductive polymer.
5. The multicolor electroluminescent element according to claim 1,
wherein at least one of the first and the third electrode layer is
vapor deposited onto the substrate.
6. The multicolor electroluminescent element according to claim 1,
wherein at least one of the first and third electrode layer at
least predominantly comprises indium-tin oxide.
7. The multicolor electroluminescent element according to claim 1,
comprising an insulating layer, which is transparent over at least
a part of its area, situated on a side of the fourth electrode
layer facing away from the substrate.
8. The multicolor electroluminescent element according to claim 1,
comprising an insulating layer situated on a side of the second
electrode layer facing away from the substrate.
9. The multicolor electroluminescent element according to claim 1,
wherein the substrate at least predominantly consists of
polyethylene terephthalate.
10. The multicolor electroluminescent element according to claim 1,
which has at least one color-filtering layers.
11. The multicolor electroluminescent element according to claim
10, wherein the substrate has color-filtering components.
12. The multicolor electroluminescent element according to claim 1,
wherein the electroluminophores incorporated in the first
electroluminescent layer have a different emission color than the
electroluminophores incorporated in the second electroluminescent
layer.
13. The multicolor electroluminescent element according to claim 1,
wherein at least one of the first and the third electrode layer is
sputtered onto the substrate.
14. The multicolor electroluminescent element according to claim 1,
which has at least one color-converting layer.
15. The multicolor electroluminescent element according to claim
14, wherein the substrate has color-converting components.
Description
[0001] The present invention relates to a multicolor
electroluminescent element.
[0002] Electroluminescence technology has increasingly gained in
significance in recent time. It allows the implementation of nearly
arbitrarily large homogeneous luminescent surfaces which are free
of screens and shadows. The power consumption and overall depth (in
the magnitude of a millimeter or less) are extremely low. In
addition to the background illumination of monochrome liquid
crystal displays, typical applications include the backlighting of
transparent films which are provided with inscriptions and/or
graphic motifs.
[0003] Electroluminescence (in short: EL) is understood as the
direct luminescent excitation of luminescent pigments and/or
luminophores by an electrical AC field. Electroluminescent elements
(in short: EL elements) based on thick-film technology using
inorganic luminescent pigments and/or luminophores and AC voltage
excitation have become widespread. Thick-film EL elements are less
complex and thus more cost-effective to produce than thin-film EL
elements.
[0004] The luminescent pigments and/or luminophores are embedded in
a transparent organic or ceramic binder. Starting materials are
typically zinc sulfides, which generate different, relatively
narrow-band emission spectra as a function of doping or co-doping
and preparation procedure. The focal point of the spectrum
determines the particular color of the emitted light.
[0005] The exciting AC voltage field typically has a frequency of a
few hundred hertz, the effective value of the operating voltage
frequently being in a range from approximately 50 to 150 volts. By
elevating the voltage, a higher light density may normally be
achieved, which is typically in a range from approximately 50 to
approximately 200 candela per square meter. Elevating the frequency
usually causes a color shift toward lower wavelengths. Both
parameters must be tailored to one another in order to achieve a
desired light impression, however.
[0006] In principle, two types of electrodes suggest themselves
above all for the production of typical thick-film EL elements
using AC voltage excitation. One type are indium-tin oxide
electrodes (ITO) which are sputtered or vapor-deposited onto
plastic films in vacuum. They are very thin (a few hundred
angstroms) and offer the advantage of high transparency at a
relatively low resistance per unit area (approximately 60 to 600
ohms/square). In addition, printing pastes having ITO or ATO
(antimony-tin oxides) or conductive transparent polymer pastes may
be used. At a thickness of approximately 5 to 20 .mu.m, electrodes
of this type offer only lesser transparency at a high resistance
per unit area (up to 50 kohm/square). However, they may be applied
having largely any arbitrary texture, even onto textured surfaces.
Furthermore, they offer a relatively good laminating ability as
well as restricted ability to be deformed.
[0007] The service life of an EL element is limited. It is a
function above all of the level and frequency of the AC voltage
applied, in addition, however, also environmental influences, in
particular the effect of moisture and UV radiation. The service
life of an EL element is typically specified as a half-life value
of the luminescent pigments. This is the time after which the
luminance has been reduced to half of the starting value under the
influence of the electrical field with unchanged operating
conditions. In practice, the luminance falls to half of the
original value within approximately 2000 to 3000 hours of
operation.
[0008] The emission color of an EL element may be tailored to the
desired color impression through multiple possible measures. These
include doping and co-doping of the luminescent pigments, mixing
two or more EL pigments, adding one or more organic and/or
inorganic color-converting and/or color-filtering pigments, coating
the EL element using organic and/or inorganic color-converting
and/or color-filtering substances, adding colorants to the polymer
matrix in which the luminescent pigments are dispersed, and
incorporating a color-converting and/or color-filtering layer or
film in the structure of the EL element.
[0009] There is frequently a need for EL elements which may
luminesce multicolored, i.e., alternately in different colors as a
function of an external controller. Corresponding EL elements are
referred to as multicolor electroluminescent elements.
[0010] Multicolor electroluminescent elements are known, inter
alia, from EP-A-1045618. A multicolor EL lamp is described therein,
in which different colors result through additive color mixing, in
that at least two electroluminescent layers containing luminescent
pigments which lie one on top of another are activated
appropriately using at least three electrode layers. The first
electrode is produced for this purpose using vapor deposition of
ITO on a PET substrate, while in contrast all further layers, i.e.,
also all further electrodes, are produced using screen
printing.
[0011] A multilayer EL element having different patterns and many
luminescence colors is also described in EP-A-0998171. The first
transparent electrode is also produced here on a PET film using
vapor deposition or sputtering. All further electrodes are produced
using printing of optically transparent pastes.
[0012] A multicolor EL element which has multiple light-transparent
electrode layers and multiple luminescent layers having different
colors is known from EP-A-0973358. A multilayer structure produced
by printing is also implemented according to this publication.
[0013] The structure having multiple luminescent layers produced
using screen printing, which all known multicolor EL elements
listed share in principle, is connected to some problems. In
industrially typical and available electroluminophores, particle
diameters of greater than 20 micrometers, typically between 20 and
35 micrometers, and a broad particle size distribution must
normally be expected. Therefore, luminescent layer thicknesses of
40 to 60 .mu.m are typical. If coarse-grained pigments of this type
are dispersed in screenprinting inks and applied in multiple layers
to a carrier substrate, it is obvious that at typical degrees of
filling of 65 to 75 weight-percent, a very uneven surface results.
The unevenness is caused by the spread of the particle dimensions
and, in addition, by the evaporation of solvent during the drying
procedure. The unevenness of the surface of each individual layer
may be reduced, for example, by using UV-curable polymer binders
and/or by using fine-grain luminescent pigments and/or luminescent
pigments having a narrower particle size distribution. These
problems may thus be controlled in EL elements which are only
provided with only one luminescent layer and thus emit
monochromatically. However, in multilayer structures, the
unevenness of the individual layers adds up randomly, so that
multicolor EL elements providing a homogeneous light impression are
not producible or are only producible with significant discards in
the way described in practice.
[0014] Furthermore, an additional leveling printing procedure
and/or a leveling lamination procedure may be performed. However,
for typical EL elements the disadvantages of process steps of this
type outweigh their advantages, since each additional layer reduces
the electrical AC field applied, and projecting pigment particles
may be pressed into the polymer layer underneath during a
lamination procedure, but may just as well penetrate the dielectric
insulation and thus influence the function of the particular EL
element very disadvantageously.
[0015] In addition to these problems of unevenness, there is also
the need to guide the individual planar electrodes to typically
laterally situated terminal areas. This results in layer height of
over 100 .mu.m having to be overcome in a multilayered structure
produced through screen printing on a substrate, which may not be
achieved using ITO or ETO screen printing inks through single
printing and results in a further elevation of the unevenness of
the surface through the use of busbar printed formations using
silver pastes. This is because even with a single luminescent layer
of the above-mentioned typical thickness, insulating layers or
dielectric layers must be guided very carefully over the layer
edges in order to also be able to guide a rear electrode having
good electrical conduction properties over a layer edge of this
type.
[0016] Therefore, the overall production of typical multicolor EL
elements, but particularly the production of the electrical
circuitry and/or the terminals of diverse fields, is extremely
difficult to control and very susceptible to errors in luminescent
layers having segmented structures.
[0017] In consideration of the set of problems described, it is the
object of the present invention to provide a multicolor
electroluminescent element which may assume different luminescent
colors as a function of the electrical activation and is
nonetheless producible at acceptable outlay in high quality.
[0018] This object is achieved according to one aspect of the
present invention by a multicolor electroluminescent element
according to Claim 1.
[0019] EL elements according to the present invention thus differ
from the prior art in that the electroluminescent capacitors each
having one electroluminescent layer and two electrode layers are
situated on both sides of a film substrate. In a multicolor EL
element having two electroluminescent capacitors, the structure on
one particular side of the film substrate is thus not more complex
than in a typical monochromatically emitting EL element. The set of
problems of unevenness described above, which grows with a greater
number of layers situated one on top of another, is thus
minimized.
[0020] Preferred embodiments of the multicolor EL element according
to the present invention may be implemented according to Claims 2
through 11.
[0021] The possible uses of multicolor EL elements according to the
present invention are manifold. For example, the background
illumination of displays having illumination colors selectable by
the user, the different-colored illumination of multifunction
operating elements depending on the operating mode in the field of
automobiles, for example, advertising displays backlit using
changing colors, etc., are conceivable. Multicolor EL elements
according to the present invention are very well suitable for
representing switching actions (e.g., color change from "on" to
"off" through alternate control of the operating voltage to two EL
capacitors emitting in different colors). Multiple different colors
may be produced through additive color mixing if the different
electroluminescent capacitors may each be supplied using multistage
or continuously adjustable operating voltage.
[0022] If three electroluminescent layers emitting in different
colors are required, for example, to provide an RGB system
(red/green/blue) capable of displaying the entire color spectrum,
above all two types of alternatives are conceivable. Firstly, an EL
element according to the present invention having front and rear
electroluminescent capacitors may be combined with a typical,
transparently implemented EL element only having one
electroluminescent capacitor. In addition, one side of a film
substrate may be provided with a structure containing one
electroluminescent capacitor and the other side may be provided
with a structure containing two electroluminescent capacitors. The
problems cited of increasing unevenness and difficult wiring occur
again, however, with two electroluminescent capacitors lying one on
top of another, these problems may be handled in principle,
although with the above restrictions. In contrast, three
electroluminescent capacitors situated one on top of another on the
same side of a film substrate--as an RGB structure according to the
prior art would appear--may hardly still be technically implemented
at acceptable quality.
[0023] An example of a preferred embodiment of the present
invention is explained in greater detail on the basis of the
attached drawing.
[0024] FIG. 1 is a purely schematic cross-sectional illustration of
the detail of a multicolor EL element according to the present
invention. The area of the electrode terminals is not shown. The
illustration is not to scale; in particular, layer thicknesses are
greatly enlarged for reasons of clarity. The viewing side, i.e.,
the side in whose direction light is to be emitted, is on top in
the drawing.
[0025] The EL element has a transparent plastic film substrate 1,
on whose rear side a transparent first electrode layer 2 made of
ITO is sputtered or vapor-deposited in vacuum. The materials
suitable for the plastic film substrate 1 are manifold, depending
on the application, such as polycarbonate (PC), polyalkylene
terephthalates, polyamide (PA), polyacrylate, polymethacrylate,
polymethyl methacrylate (PMMA), polyurethane (PUR),
polyoxymethylene (POM), polyethylene (PE), polypropylene (PP),
polystyrene (PS), polyvinyl chloride (PVC), polyamide (PI),
polyetherimidene (PEI), polyether, polyether ketones (PEK),
polyvinyl fluoride (PVF), polyvinylidene fluoride (PVdF), or
similar films, which have a high transparency in the optically
visible wavelength range. Films made of polyethylene terephthalate
(PET) are especially suitable. Depending on the desired color
effect, the plastic film substrate 1 may also contain a colorant
and/or color-converting substances. In principle, the substrate 1
may also comprise a material other than a plastic film which is at
least transparent.
[0026] A first electroluminescent layer 3 having dispersed
electroluminophores is situated on the first electrode layer 2,
this being a transparent matrix 5 in which the electroluminophores
4 are incorporated. The first electroluminescent layer 3 may be
implemented as a cast or extruded film, but also as a screenprinted
layer or the like. The illustration of the electroluminophores 4 in
particular is to be seen as purely schematic. In practice, the
particles are to approximate a spherical shape as much as possible.
Electroluminophores are typically sensitive to the effects of
moisture. Therefore, additional layers may be integrated, which
assume the function of a moisture barrier or vapor barrier.
However, these may be largely dispensed with if microencapsulated
electroluminophores 4 are used in particular. The
microencapsulation is typically oxidic or nitridic, but an organic
microencapsulation or a diamond-like carbon encapsulation is also
conceivable, for example.
[0027] The second electrode layer (rear electrode layer) 6, which
is insulated using the insulating layer 7 on its side facing away
from the first electroluminescent layer 3, is situated on the first
electroluminescent layer 3 or an insulating intermediate layer (not
shown) located thereon.
[0028] The rear electrode layer 6 may be produced through
doctoring, roller coating, curtain casting, spraying, or printing
(usually using screen printing) in the form of an intrinsically
conductive polymer layer and/or a layer having metal oxides, such
as indium-tin oxide (ITO) or antimony-tin oxides (ATO). However,
because of its good conductivity and reflection properties, an
electrode layer containing silver is especially suitable as the
rear electrode layer.
[0029] The insulating layer 7 may be a thin lacquer layer or the
like, however, an insulating plastic film may also be laminated on
in addition to or instead of this layer.
[0030] The EL element shown has a self-adhesive coating 12 on its
side facing away from the viewing side, using which it may be
attached easily to greatly varying surfaces. Of course, with other
types of attachment, such as a clamp attachment, the self-adhesive
coating may be dispensed with.
[0031] On the front side, i.e., on the viewing side, a third
electrode layer 8 made of transparent conductive lacquer is applied
to the plastic film substrate 1. This may be a doped polythiophene
(trade name Orgacon [registered trademark of the Agfa-Gevaert
group]). Alternatively, a multicolor EL element according to the
present invention may also be produced starting from a plastic film
substrate 1 sputtered or vapor-deposited on both sides using ITO.
In this case, the third electrode layer 8 comprises ITO, like the
first electrode layer 2.
[0032] A second electroluminescent layer 9 having dispersed
electroluminophores 4 is situated on the third electrode layer 8,
this again being a transparent matrix 5 in which the
electroluminophores 4 are incorporated. The second
electroluminescent layer 9 may also be implemented as a film,
screenprinted layer, or the like.
[0033] The fourth electrode layer 10 made of transparent conductive
lacquer (e.g., a polythiophene), which is insulated on the viewing
side using an insulating layer 11, is situated on the second
electroluminescent layer 9 or an insulating intermediate layer (not
shown) located thereon.
[0034] The EL element may be covered partially opaque on the
viewing side, for example, using an imprint or additionally
provided cover elements, to implement symbols, inscriptions,
etc.
[0035] Depending on the intended use, one or more of the electrode
layers 2, 6, 8, 10 may also be provided over part of the area
and/or segmented. Instead of a continuous area, there are then one
or more partial areas, which may each be wired separately and thus
activated individually. For example, using screen printing
technologies known per se, one or both electroluminescent layers 5,
9 may be provided in segments with electroluminophores 4 emitting
in different colors to achieve areas luminescing locally in
different colors.
[0036] In particular in large-area embodiments, it is suggested
that the electrode layers 2, 6, 8, 10 be contacted via busbars,
i.e., highly conductive structures made of silver and/or copper
and/or carbon pastes or the like around the edge and/or around the
border.
* * * * *